This disclosure pertains to a reduced dark current barrier-type photo-detector that is comprised of a doped semiconductor layer, a barrier, and metal contacts disposed on the barrier where the doped semiconductor layer is used for photo-absorption and the effective conduction and valance band alignments for the doped semiconductor layer and barrier are arranged so as to allow photo-generated minority carrier flow to the contacts but filter or block majority carrier flow. Individual elements (e.g., pixels) in the photo-detector array may be defined by the metal contacts disposed on the barrier. The harrier, however, may be preserved such that it extends beyond the extent of the defined pixel areas. Although applicable to a wide range of barrier-type photo-detector, the exemplary embodiments and associated energy band diagrams presented in this disclosure depict an nBm barrier-type photo-detector. The structures and methods discussed herein, however apply as well to pBm (e.g., p-doped) structures. The “m” in this case stands for the metal disposed on the barrier to define readout pixels.
An embodiment of an exemplary nBn structure electron band diagram is illustrated in FIG. 1. The embodiment represents an embodiment of the concepts described in U.S. Pat. No. 8,044,435. The underlying concept relates to driving minority carriers from a photo absorbing layer 1000 to a contact region 1020 through a barrier 1010 where the compositions of the absorber layer, barrier, and contact layers are such that minority carriers can penetrate the barrier 1010 but majority carriers cannot. As can be seen in FIG. 2 and as discussed in U.S. Pat. No. 8,044,435,the pixels in the contact layer 2030 are isolated by etching down to, but not through, the barrier 2010 in order to accomplish pixel delineation. In the embodiment shown, each pixel is associated with a contact 2040 and a read-out interconnect point 2080. Minority carriers generated in the absorber layer 2000 pass through the barrier 2010 and into the contact layer 2030 where they are read-out through the interconnect 2080 via the contact 2040. This process complicates focal plane array structure and fabrication by requiring additional etch and passivation steps. This fabrication process results in etched mesas, which can contribute excessive dark current for small area devices.
It would be an improvement in terms of performance, manufacturability, reliability, versatility and production yield to delineate and isolate pixels in such a photo-detector in ways other than material removal. It would also be an improvement in terms of performance, manufacturability, reliability, versatility, and production yield to delineate and isolate pixels without the need for a contact layer.